The invention relates to a coupling element, comprising a light source and a (lens-shaped element). The light source is mounted on a support on which a cover is secured. The lens is situated opposite the light source in the path of the light beam emitted from the source. The light beam is directed transverse to the support.
A coupling element of this kind is described in an article entitled "High-Efficiency Long-Lived GaAlAs LED's for Fiber-Optical Communication" by Masayuki Abe et al. (IEEE Transactions on Electron Devices, Vol. ED-24, No. 7, July 1977, pages 990-994). The described coupling element makes use of a light-emitting diode, but could alternatively use a semiconductor laser as the light source. Furthermore, the lens is an end of an optical fiber in which the light generated by the diode is radiated.
The coupling element described in the above-mentioned article is used in an optical communications system where data is transmitted by means of light pulses. The light pulses are transmitted via optical fibers. However, besides the lens on the end of the optical fiber, the coupling element may also include other optical elements such as lenses, semitransparent mirrors, etc. A coupling element of this kind can be used, for example, in a video or audio disc/reading device (also referred to as Video Long Play and Audio Long Play apparatus, respectively) in which the data stored on a disc is read optically. The means for optically reading the data on the disc includes at least the light source, the lens, a reflective surface of the video/audio disc, and a light detector.
In order to maximize the transmission of light to the optical element situated behind the lens, the lens should be situated at an optimum position and at an optimum distance with respect to the light source. The above-mentioned article describes how to adjust the two optical elements to the optimum positions and distance.
During the adjustment produce, the amount of light radiated into the fiber via the lens is measured. The cover, in which the optical fiber is secured by means of an epoxy resin, is displaced with respect to the support until the amount of light measured is maximum. The cover is then maintained in this position until the epoxy resin used for securing the cover to the support has set; this is a drawback in view of the time required for manufacturing the coupling element. Furthermore, the space between the cover and the support is contaminated by the solvents released during the setting of the epoxy resin. Consequently, the semiconductor light source cannot be provided in either an evacuated space or a space filled with an inert gas.